Electrode structure



Defi 1935 s. F. ESSIG.

ELECTRODE STRUCTURE Filed Feb. 24, 1952 16a 4 18a 34 20a,

. nvvm TOE: SanflrdEEssig H/SATTOF/VEK Patented Dec. 29 1936 UNITED STATES ELECTRODE STRUCTURE SanfordfF. Essig, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application February 24, 1932, Serial No. 594,779

25 Claims.

My invention relates to improvements in methods of making mosaic electrode structure of the general type used in cathode ray apparatus for developing picture signals in the art of television, an example of which i's described in detail in the copending application of Vladimir K. Zwory'kin, filed May 1, 1930, hearing Serial No. 448,834, and assigned to the Westinghouse Electric and Manufacturing Company.

Mosaic electrode structure of the character referred to comprises an insulating supporting base'member to which are applied or which carries individual, minute, photosensitive, electri- 'callyconductive elements insulated from each other and spaced uniformly apart. In operation of the cathode ray apparatus, the object to be transmitted is illuminated and an image thereof is projected onto the photosensitive surface of the mosaic structure. Electron emission then to scan the surface thereof at the rate of 16 to 20 times persecond. The eifectiveness of the apparatus in-developing picture signals, which correspond faithfully with the light image of the object, is dependent in large part upon the capability of the minute individual elements to store up linearly and retain their electrostatic charges until they are struck by the electron ray.

. The fidelity of reproduction is interfered with if there is any appreciable leakage between the adjacent elements or particles, and it is this difliculty which has been encountered in the many and various constructions proposed heretofore. This dimculty is enhanced by the fact that the individual particles must be very small and closely spaced to produce sufficient detail, together with the fact that the choice of materials and the construction in general are limited and must take into account the process to which the mosaic structure is subjected before takes place from the individual elements inway of eliminating leakage between the individual particles has been further increased on account of the fact that the methods of doing this have resulted in loss of desirable operating characteristics of the structure, such as in the. photosensitivity of the particles.

With the foregoing in mind, it is one of the objects of my invention to provide an improved method of making a mosaic electrode structure of the character referred to which avoids the difliculties encountered heretofore and by which an eilicient structure is provided wherein the individual particles for storing'up the electrostatic charges are sufficiently small and closely spaced for satisfactory operating action, wherein there is negligible leakage between the ad jacent particles, and wherein the particles, after all the manufacturing steps have been completed, have a maximum degree of photosensi -tivity.

Other objects and advantages will hereinafter appear.

In carrying out my invention, a suitable insulating base member, such as a sheet of mica or an aluminum sheet coated with a layer of aluminum-oxide, is coated on one side thereof with a thin layer of an electrically-conductive material. Heat is then applied in such degree and for such length of time as is required to develop such a surface tension in the material that individual and minute portions thereof draw up in the form of particles, droplets or globules spaced from each other, the number of particles or globules. and the average size thereof in a unit area being sufficient to satisfy the operating requirements referred to above in the way of detail of picture reproduction. This action, in other words, might be explained as a general breaking-up of the continuous film of electrically-conductive material into the individual, minute and closely spaced particles or globules.

The globules are then provided with an insulating coating which, if the material used is silver, is in the form of a silver-oxide coating over each of the silver particles or globules. The

globules are then photosensitized in any well-- known manner, during which step any leakage paths between adjacent particles or globules are removed.

In the drawing, which illustrates the various steps in the process of manufacture of a mosaic electrode structure in accordance with my invention,

Figure l is a fragmentary, perspective and highly-magnified view of the materials at the first step in the process of manufacture;

Figs. 2 and 3 are fragmentary, elevational and highly-magnified views, illustrative of the second step;

Fig. 4 isa plan view in perspective of Fig. 3, on a reduced scale; and

Figs. 5, 6, and '7 are fragmentary, sectional and highly-magnifled views, illustrative of the third, fourth and fifth steps, respectively.

More specifically, a mosaic electrode structure of the character referred to above is made, in accordance with my invention, as follows.

A silver compound, such as silver-oxide or' silver-carbonate, is applied to a supporting base member of any suitable insulating material, such as a sheet ID of mica. The silver compound may be applied by spraying, dusting, brushing, flowing, printing on to the supporting base with or without the use of a mask, or in any other suitable manner, to form a thin layer of the ..compound on one side of the mica sheet. In applying the layer of silver compound by the dusting method, it is proposed to place the mica sheet l0 under a bell jar, and inject very small particles or grains l2 of silver-oxide or silvercarbonate to form a fog, the particles then being permitted to settle onto the upper face of the mica sheet to form a film, the thickness of which is only of the order of several times the size of a grain of the compound. In this connection, the particles of the silver compound are taken from a supply made by grinding silver-oxide or silver-carbonate until the grains are of about the same size of those in talcum powder.

The mica sheet with the thin silver-coinpound is then removed, and inserted into a furnace, at

. a temperature of the order of 800 degrees centigrade, for a period of the order of 15 seconds, after which the structure is removed and allowed to cool. temperature and period of time have been found to be suflicient to substantially completely reduce the silver compound to metallic silver, and to cause the formation of minute, individual globules or particles of the silver spaced from each other and sufiicient in number per unit area to satisfy the operating requirements. During this, the second step in my improved method, it is believed that the minute ,,grains i 2 of the silver compound, closely packed to constitute in eifect a continuous, thin layer on the mica sheet, are each reduced to metallic silver and the silver particles, under the intense,

heat are first melted together to form a continuous layer I4 of metallic silver of substantially uniform thickness over the area of the mica sheet. During continued subjection of the silver to the intense heat for the remaining part of the 15-second period, it is believed that the surface tension developed in the silver reaches a point whereat the minute, adjacent portions of the silver layer, such, for example, as the portions i6, i8, 20 and 22 are caused to draw up in the" form of particles, droplets or globules l6a, l8a, 20a and 22a, respectively. In other words, the identified heat application causes the adjacent portions of the silver layer to break away from each other and form the minute, individual, spaced, silver particles or globules and thousands of other globules 24.

The next and third step in the present exemplification of my invention consists in oxidation of the silver particles or globules to form on each an insulating oxide film of definite thickness.

To this end, the structure is mounted in the ray apparatus, the tube is evacuated, and oxygen admitted in sufllcient amount to completely carry out the oxidation step. In some cases, it has been determined that oxygen at a pressure of one tenth of a millimeter of mercury is adequate for this purpose. The electrode structure is then subjected to a high-frequency field of suillcient intensity to cause ionization of the oxygen atoms. This action causes a film 26 of silver-oxide of definite thickness to form on each of the silver globules.

The next and fourth step consists in photosensitizing each of the oxidized silver particles or globules, for which purpose the tube is evacuated to remove any residual oxygen, and a caesium .capsule previously mounted in the container, is

exploded. This step causes deposition of caesium,

28 on each of the oxidized silver globules, but the amount of caesium on each is in excess of that conducive to maximum photosensitivity. Furthermore, during this step, a certain amount of free caesium 30 condenses on the supporting mica sheet In between the individual particles or globules, and constitutes what in effect would be leakage paths between the adjacent particles or globules of sufficient conductivity to interfere materially with the operating action.

One of the important steps in my present improved method is the removal of this free caesium condensate between the oxidized silver particles and the concurrent removal of the excess caesium on the particles or globules so that the latter have substantially the maximum degree of photosensltivity at the completion of this, the fifth step. For this purpose, the tube is connected to a continuously-operating highvacuum pump, and baked at a temperature of from 200 to 225 degrees centigrade until the particles or globules have substantially the maximum degree of photosensitivity, as indicated by effecting such further removal of the caesium on the latter as to appreciably change the degree of photosensltivity thereof. In carrying out this step, it is proposed to reduce the temperature, as explained, at a time just preceding that at which the particles or globules would have the maximum degree of photosensitivity, and to rely upon the second period of baking atthe lower temperature to cause removal of the very small amount of caesium necessary to bring the photosensitivity of the particles to the highest point.

In other words, during the first baking period at the higher temperature, the excess caesium on the globules or particles, as indicated in Fig. 6, is quickly removed to bring the globules or particles to substantially the point. of maximum sensitivity, whereat the caesium layer over the globules 24 is substantially at atomic thickness, as indicated in Fig. 'l, and most of the free caesium 30 on the mica sheet between the adjacent particles is also removed and pumped away. During the secondand relatively long baking period at the lower temperature, any slight amount of free caesium which might still be present between the globules or particles, is

removedwithout' causing any appreciable and 7 may be varied over a substantial range, de-

undesirable further removal of caesium from the particles such as would decrease their photosensitivity from the desired maximum point.

During the entire baking period, the usual metal electron gun disposed in the neck of the tube is maintained, by a high-frequency field, at a temperature sufficiently above that at which caesium begins to vaporize, thereby preventing condensation of the caesium vapor on the metal parts of the gun.

After this step, the operation is completed, and the tube is sealed off.

When it occurs that, after the second step in my improved method, during which the $11-' ver compound is reduced to a metallic silver and the individual silver particles or globules 24 caused to form on the mica sheet as illustrated in Fig. 4, the number of particles or globules I per unit area is not sufficient to meet operating requirements, it is proposed to repeat this step comprising the operations of dusting on a layer of the silver compound and reducing this to silver in the form of the individual particles or built up somewhat with new silver. After the second step has been repeated the desired number of times, the third step of oxidation of the globules and the fourth and fifth steps, for photosensitizing the latter, are carried out as explained.

Instead of using a metallic compound in carrying out the first step, the pure metal may be applied directly to form a film on the'insulating base member. This may be done in any suitable manner such as by chemical deposition by the so-called Brashear process, by evaporation in a vacuum from a molten bead of the metal, by sputtering in 'a partial vacuum. This also may be done by the so-called Schoop process of spraying with the metal. The second step and the remaining oxidizing and photosensitizing steps are then carried out as before explained.

With regard to the specific values of temperature, pressure and time given above, it will be understood that these have been given merely by way of illustration, and that the same are not critical in any strict sense of the word and pending upon particular conditions. These values, however, should be such that the final result is the production of individual, substantially uniformly spaced, electrically-conductive and photosensitive globules or particles, insulated from each other,- and each of such size as to have a capacity to ground suflicient to store up the electrostatic charge during any picture frame period. In this connection, reference is made to the copending application of Vladimir. K. Zworykin, Serial No. 468,610, filed July 17, 1930, and assigned to the RCA Victor Company.

From the foregoing, it will be seen that I have provided an improved method of making a mosaic electrode structure wherein the individual, electrically-conductive and photosensitive globules or particles are suflicient in number per unit area to meet the operating requirements for fidelity of picture reproduction, wherein there are no deleterious leakage paths between ad- I claim as my invention:

1. The process of forming a mosaic light sensitive surface on a non-conducting base which comprises applying a metal compound to the base, reducing the compound to form isolated metallic particles microscopic in size by. the application of heat, applying a layer of alkali metal upon the surface of the base and then removing the alkali metal between the particles.

2.The process of forming a mosaic light sensitive surface on an insulating base which comprises applying a metal compound to the base, reducing the compound to isolated metallic particles microscopic. in size by heating the base and compound, applying a layer of alkali metal upon the surface of the base, and then again heating the said surface to remove the alkali metal in the areas between the individual particles.

'3. The process of forming a mosaic light sensitive surface on an insulating base which comprises coating a metal compound upon the base, reducing said compound to isolated metallic particles each microscopic in size, oxidizing the surfaces of the metallic particles so produced,

applying a layer of alkali metal upon the oxidized surface and removing the tween the particles.

5. The process of forming a mosaic light sensitive surface on an insulating base which com prises applying a metal compound to the base, reducing said compound to isolated .metallic particles each microscopic in size, applying a layer of alkali metal upon the surface of the base, sensitizing the surface by heating at a temperature of the order of 225 C., and subsequently heating the surface at a temperature of the order of C. to remove any free alkali metal between the particles.

6. The steps in the method of preparing a cathode ray tube having a mosaic electrode structure having isolated microscopic particles supported upon fan insulating base and mounted within a cathode ray tube to be photosensitized which comprise the steps of' depositing a layer of alkali metal coating the particles only, and maintaining, during the period inwhichthealkali metal is deposited, the cathode ray source within thetube at a temperature above the vaporizing alkali metal be- ,temperature of the photosensitive alkali metal.

7. In the method claimed in the preceding claim the additional steps comprising subjecting the cathode ray gun within the tube during the period of depositing the alkali metal to a high frequency field.

8. A mosaic photosensitive electrode structure which comprises an insulating base, a plurality of isolated metallic particles microscopic in size formed upon the insulating base, an oxide layer upon each isolated particle, and a photosensitive material upon the oxide layer formed upon the particles only."

9. The process of forming a mosaic light sensitive surface on a heat resisting nonconducting base which comprises applying a metal compound to the base, heating the heat resisting non-conducting base surface and the metal compound to a temperature of the order of 800 C. to reduce the compound to a metal so as to thereby form on the base isolated metallic particles each of minute size, applying a layer of alkali metal upon the entire surface and subsequently heating the surface at a reduced temperature to remove the alkali metal between the'particles.

10. The process of forming a mosaic light sensitive surface on a heat resisting nonconducting base which comprises applying a metal compound to the base, heating the heat resisting non-conducting base surface and the metal compound to a temperature of the order of 800- C. for the time period of the order of seconds to reduce the compound to a metal soas -to thereby form on the base isolated metallic particles each of minute size, applying a layer of alkali metal upon the entire surface and subsequently heating the entire alkali metal coated surface to remove the alkali metal between the particles.

11'. The process of forming a mosaic light formation of said microscopic sired sensitive surface on a heat resisting nonconducting base which comprises applying a metal compound to the base, heating the heat resisting non-conducting surface and the metal compound to a temperature of the order of. 800 C. for a time period of the order of seconds to reduce the compound to a metal so as to form on the base isolated metallic particles each of minute size, oxidizing the isolated metallic particles to form on each an insulating oxide film of predetermined thickness, of alkali metal upon theentire surface and applying a layer subsequently heating the entire surface to remove the alkali metal between the particles.

12. The steps in the process of forming a mosaic surface upon an insulating base which comprise applyingto the base a material from which through heat treatment microscopic particles of electrically conductive material may be derived and then applying heat of sufficient intensity to the coated base to ca'rry'the temperature of the base surface to a value of the order of 800 C. within a time period of the order of seconds to form a plurality of microscopic sized particles each isolated one from the other.

13. The process of forming sensitive surface on a non-conducting base whichcomprises applying to the non-conducting base a material from which through heat treatment particles of microscopic size of electrically conductive material may be derived, heating the"coated base member to cause the I particles each isolated one from the other, applying a layer of alkali metal upon the entiresurface and then removing the alkali metal between the produced isolated microscopic sized electrically conductive particles.

a mosaic light 14. A mosaic photo-sensitive electrode struc- I h ture which comprises an insulating base. a plurality of isolated metallic particles each microscopic 15. The steps in the process of forming a mosaic surface on an insulating base which comprise applying a metal compound to the base and then reducing the compound to a plurality in size formed upon the insulating base, said parof isolated metallic particles microscopic in size upon the base by the application of heat, the temperature of the surface of the insulating base being limited to a value of the order of 800* C. for a time period not exceeding fifteen seconds.

16. Theprocess of forming a mosaic surface of isolated metallic particles each microscopic in size upon the base by the application of heat of a value to raise quickly the temperature of the base surface and the compound to that point whereat the surface tension of the metal formed by the-decomposition of the compound is greater than the adhesion of 'the metal to the base surface? f H a 18. A mosaic photosensitivewlectrode struc-' ture which comprises an insulating base, a plu rality of isolated metallic particles each microscopic in size formedfupon the insulating base, said metallic particles being substantially inactive under normal conditions of temperature and V -pressure and formed from the metal in which the surface tension is greater than the molecular adhesion to the base,\and a photosensitive'material coating the particles 0 19. The steps in the process of forming a mosaic surface on a, heat resisting. insulating base which comprise" applying to the base a material from which through heat treatment microscopic size particles of electrically conducting material may be derived, the said material having a melting point higher than 800 C., then heating the heat resisting insulated base surface and the material to a temperature of the order of 800 C. to form on the base a plurality of isolated particles each of microscopic size, and limiting the duration of heating to a time period of the order of 15 seconds.

20. The steps in the process of forming a mosaic on an insulating base member which comprise applying a metal compound to the base, then heating the insulating base surface and the metal compound to a temperature of the order of 800 C. to-reduce the compound to a metal and thereby to form on the basea plurality of isolated particles each ofminute size, and dis continuing the heating upon the formation of the isolated particles by heat reduction.

21. The steps in the process of forming a mosaic electrode surface .on a mica base which comprises applying an electrically conducting metal to the and heating the metal to a temperature approximating its melting po'int to form a pluralitybf isolated particles each of microscopic size: J

22.. The steps in the process of forming a 'mosaicxelectrode "surface on an insulating base to form a plurality of isolated particles each of microscopic size and coating the isolated particles only with a photosensitive material.

23. The steps in the process of forming a mosaic electrode surface on an insulating base which include applying an electrically conducting metal to the base, heating the metal to cause the formation of a plurality of isolated metallic particles each of microscopic size upon the base, applying photoelectric material to the surface subsequent to the production of the isolated particles thereupon and removing the photoelectric material in the area between the isolated particles.

24. The process of forming a mosaic lightsensitive surface on a nonconducting base which comprises applying an electrically conducting material to the base to cover substantially the r entire area of the base, heating the material to cause the formation of a plurality of isolated metallic particles each of microscopic size upon the base, coating the surface of the base and the microscopic sized particles with photoelectric material, and removing by the application of heat the photoelectric material from the base in the area between the isolated particles.

25. The process of forming a mosaic light sensitive surface on a non-conducting base which comprises applying to the base a metallic coating, thermally converting the metallic coating into a plurality of isolated metallic particles each microscopic in size upon the base, and photosensitizing the individual isolated metallic particles.

SANFORD F. ESSIG. 

